Dokuchaevite, ideally Cu8O2(VO4)3Cl3, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Dokuchaevite occurs on the crusts of various copper sulfate exhalative minerals (such as kamchatkite and euchlorine) as individual prismatic crystals. Dokuchaevite is triclinic, P$\bar{1}$, a = 6.332(3), b = 8.204(4), c = 15.562(8) Å, α = 90.498(8), β = 97.173(7), γ = 90.896(13)°, V = 801.9(7) Å3 and R1 = 0.057. The eight strongest lines of the X-ray powder diffraction pattern are (d, Å (I)(hkl): (15.4396)(18)(00$\bar{1}$), (7.2762)(27)(0$\bar{1}$1), (5.5957)(43)(012), (4.8571)(33)($\bar{1}\bar{1}$1), (3.1929) (29)(023), (2.7915)(30)(202), (2.5645)(21)(032), (2.5220)(100)(1$\bar{3}$0), (2.4906)(18)(130) and (2.3267)(71)(2$\bar{2}$2). The chemical composition determined by electron-microprobe analysis is (wt.%): CuO 60.87, ZnO 0.50, FeO 0.36, V2O5 19.85, As2O5 6.96, SO3 0.44, MoO3 1.41, SiO2 0.20, P2O5 0.22, Cl 10.66, –O = Cl2 2.41, total 99.06. The empirical formula calculated on the basis of 17 anions per formula unit is (Cu7.72Zn0.06Fe0.05)Σ7.83(V2.20As0.61Mo0.10S0.06P0.03Si0.03)Σ3.03O13.96Cl3.04.

The crystal structure of dokuchaevite represents a new structure type with eight Cu sites, which demonstrate the remarkable diversity of Cu2+ mixed-ligand coordination environments. The crystal structure of dokuchaevite is based on OCu4 tetrahedra that share common corners thus forming [O2Cu6]8+ single chains. Two of the eight symmetrically independent copper atoms do not form Cu–O bonds with additional oxygen atoms, and thus are not part of the OCu4 tetrahedra, but provide the three-dimensional integrity of the [O2Cu6]8+ chains into a framework. TO4 mixed tetrahedral groups are located within the cavities of the framework. The structural formula of dokuchaevite can be represented as Cu2[Cu6O2](VO4)3Cl3.

Yellow needles of 'iodolaurionite', Pb(OH)I, and a novel compound Pb2O(OH)I, have been prepared by hydrothermal reactions of PbO and PbI2 at 170°C. The crystal structure of 'iodolaurionite', Pb(OH)I (orthorhombic, Pnma, a = 7.8244(8), b = 4.2107(4), c = 10.4724(10) Å, V = 345.03(6) Å3, Z = 4) has been refined to R1 = 0.041 for 129 independent observed reflections. The structure is based on the OHPb3 triangles sharing common edges to produce single [OHPb]+ chains extending along the b axis and parallel to the ab plane. The three-dimensional integrity of the structure is provided by the Pb–I bonds and the O–H···I hydrogen bonding. The structure is isotypic with that of laurionite, Pb(OH)Cl. The crystal structure of Pb2O(OH)I (monoclinic, C2/m, a = 13.711(3), b = 4.0975(10), c = 9.584(2) Å, β = 110.64(1)°, V = 503.9(2) Å3, Z = 4), has been solved by direct methods and refined to R1 = 0.053 for 586 independent observed reflections. In the structure of Pb2O(OH)I, O(1)Pb4 tetrahedra link together by sharing edges and corners to form [OPb2]2+ chains similar to those observed in sidpietersite. The O(2) atoms belong to hydroxyl groups attached to both sides of the chains to produce novel [O(OH)Pb2]+ 1D units. The [O(OH)Pb2]+ units are extended parallel to the b axis and lie within the bc plane. The [O(OH)Pb2]+ units are linked together via hydrogen bonding in the (100) plane and by weak Pb–I bonds in the [100] direction. The [O(OH)Pb2]+ bands can be obtained from the [OPb] layer of OPb4 tetrahedra present in the structure of tetragonal PbO (litharge). The continuous [OPb] layer has to be broken into [O2Pb2] bands containing 3- and 4-coordinated O atoms in the 1:1 ratio with subsequent protonation of the 3-coordinated O sites. Relations of Pb(OH)I and Pb2O(OH)I to known Pb hydroxy- and oxyhalides are described briefly.

Rickturnerite, which has the ideal formula Pb7O4[Mg(OH)4](OH)Cl3, is a new mineral from Torr Works (Merehead) quarry, near the village of Cranmore in Somerset, United Kingdom. It occurs as pale emerald green to grey porous aggregates of disordered interwoven minute fibrous crystals with mereheadite, cerussite, calcite, aragonite, mimetite, hydrocerussite, “plumbonacrite” and an uncharacterized lead oxychloride, in cavities inside a manganite and pyrolusite pod. The crystals are typically less than 5 μm wide and 200 μm long, but they can reach 40 × 100 μm in cross-section and over 1 mm in length. The mineral is translucent with a vitreous lustre and each needle is brittle with an indistinct cleavage, breaking with a splintery fracture. The streak is white, the Mohs hardness ∼3 and the density calculated using the empirical formula 6.886 g cm–3. Electron microprobe analyses yielded PbO 87.7, MgO 1.79, CuO 0.14, Cl 6.62 wt.%; H2O was calculated on the basis of structural considerations as 2.27 wt.% totalling 97.02 wt.%. A charge-balanced formula, based on 12 anions, is Pb7.16Mg0.81Cu0.03Cl3.40H4.60O8.60. Rickturnerite is orthorhombic Pnma, with a = 5.8024(6), b = 22.717(2), c = 25.879(3) Å, V = 3411.2(6) Å3 and Z = 8. The diffraction pattern contains strong reflections that define a subcell with a = 5.8034(5), b = 11.3574(9), c = 12.939(2) Å, V = 852.9(6) Å3 (space group Pmm2 which is related to the real unit cell by the transformation matrix [100/020/002]), and weak reflections that correspond to doubled b and c parameters. Since the difference between the large and small cells is only in a number of split and low-occupancy positions in the disordered region of the structure we provide the description of the subcell structure. The five strongest lines in the X-ray powder diffraction pattern [listed as dobs (Å), Iobs, (hkl)] are as follows: 6.474, 100, (400); 3.233, 73, (107); 2.867, 57, (705); 5.636, 44, (011); 3.112, 31, (802). The crystal structure was solved by direct methods and refined using 1318 unique reflections to R1 = 0.063. The structure is composed of a fully ordered part consisting of double [O2Pb3]2+ chains of oxocentred [OPb4] tetrahedra extended along the b-axis, which together with Cl– ions form 2-dimensional blocks parallel to (001). In between these blocks, there is a disordered region containing ordered [Mg(OH)6]4– octahedra and low-occupancy Pb and OH sites with a slight degree of ordering; these produce the weak supercell reflections.

Detailed analysis of the crystal structures of minerals and inorganic compounds containing oxocentred [OCu4] tetrahedra reveals the following principle for relationships between oxocentred tetrahedra and tetrahedral oxyanions (Tn+O4)−(8−n) with T = S6+ or V5+, or triangular pyramidal oxyanions (SeO3)2− (which may be considered as (SeO3E)2− tetrahedra assuming the lone pair E of selenium to be a fourth ligand): (Tn+O4)−(8−n) tetrahedra are ‘attached’ to the oxocentred tetrahedra so that their grounds (O-O-O and Cu-Cu-Cu) are parallel to each other and the mutual orientation is regular (O corners are exactly under Cu corners). We propose to describe these relationships as ‘face-to-face’, meaning that the oxocentred and cation-centred tetrahedra ‘meet’ along their ‘whole’ triangular faces. Geometric characteristics of ‘face-to-face’ relationships are discussed.

The crystal structure of chloroxiphite, Pb3CuO2(OH)2Cl2, from Merehead Quarry (monoclinic, P21/m, a = 6.6972(8), b = 5.7538(5), c = 10.4686(14) Å,β = 97.747(10)°, V = 399.72(8) Å3) has been refined to R1 = 0.041. The structure contains three symmetrically unique Pb sites and one Cu site. The strong distortion of the Pb2+ coordination polyhedra is due to the stereoactivity of the s2 lone electron pairs on the Pb2+ cations. The Cu-site is coordinated by four OH- groups to form an almost planar Cu(OH)4 square that is complemented by two apical Cl– anions, forming an elongated [Cu(OH)4Cl2] octahedron. Because of the large size and variability of coordination polyhedra around Pb2+ cations and the strength of the Me–O bonds in comparison to the Me–Cl bonds (Me = metal), it is convenient to describe the structure of chloroxiphite in terms of oxocentred OPb4 tetrahedra. The O1 atom is tetrahedrally coordinated by four Pb2+ cations forming relatively short and strong O–Pb bonds. The OPb4 tetrahedra link together via common edges to form [O2Pb3]2+ double chains. The difference between chloroxiphite and other natural oxyhalides is the presence of Cu2+ cations which form an independent structural unit that links to units formed by OPb4 tetrahedra. In this sense, chloroxiphite can be considered as a modular structure consisting of both strong cation- and anion-centred units.

The crystal structures of synthetic Pb3O2(CO3) and NaPb2(OH)(CO3)2, have been solved by direct methods and refined to R = 0.062 and 0.024, respectively. Pb3O2(CO3) is orthorhombic, Pnma, a = 22.194(3), b = 9.108(1), c = 5.7405(8) Å, V = 1160.4(3) Å3, Z = 8. There are four symmetrically distinct Pb2+ cations in irregular coordination polyhedra due to the effect of stereoactive s2 lone electron pairs. The structure is based upon double [O2Pb3] chains of [O(1)Pb4] and [O(2)Pb4] oxocentred tetrahedra and CO3 groups. The [O2Pb3] chains are parallel to the c axis, whereas the CO3 groups are parallel to the (010) plane. NaPb2(OH)(CO3)2 is hexagonal, P63mc, a = 5.276(1), c = 13.474(4)Å, V = 324.8(1) Å3, Z = 2 and has been solved by direct methods. There are two symmetrically distinct Pb2+ cations in asymmetric coordination polyhedra due to the effect of stereoactive s2 lone-electron pairs. The single symmetrically unique Na+ cation is in trigonal prismatic coordination. The structure is based on hexagonal sheets of Pb atoms. Within these sheets, Pb atoms are located at vertices of a 36 net, such that each Pb atom has six adjacent Pb atoms that are ~5.3 Å away. Two sheets are stacked in a close-packing arrangement, forming layers that contain the (CO3) groups. The layers are linked by OH groups that are linearly coordinated by two Pb2+ cations. Na+ cations are located between the layers. The structure is closely related to the structures of other lead hydroxide carbonates (leadhillite, macphersonite, susannite, hydrocerussite, ‘plumbonacrite’).

Two novel copper selenite chlorides, K[Cu3O](SeO3)2Cl (I) and Na2[Cu7O2](SeO3)4Cl4 (II), have been synthesized by the CVT method. Their crystal structures have been solved by direct methods and refined by least-squares techniques. I is triclinic, space group P1̄, a = 7.6821(5), b = 8.1179(5), c = 8.7836(6) Å, α = 113.193(3), β = 108.735(4), γ = 98.245(4)°, V = 453.32(5) Å3, R1 = 0.0481 for 1210 unique reflections with F≥4σ(F); II is triclinic, space group P1̄,a = 7.4362(6), b = 8.3361(7), c = 9.1343(11) Å,α = 110.277(6), β = 106.212(6), γ = 105.158(4)°, V = 467.94(8) Å3, R1 = 0.0265 for 2498 unique reflections with F≥4σ(F). The structures of I and II can be described in terms of dimers of copper oxocentred tetrahedra. In I, two (OCu4)6+ tetrahedra share a common Cu···Cu edge to form the [O2Cu6]8+ dimer, whereas the structure of II is based upon two (OCu4)6+ tetrahedra linked together by one common Cu atom resulting in the formation of the [O2Cu7]10+ dimer. A comparison with related minerals and inorganic compounds is given.